The present invention relates to a concrete low height, or profile, weighbridge deck such as used in above-ground truck scales and is a method of construction of such weighbridge decks.
It is well known that weighing of vehicles, such as trucks, can be accomplished by means of a platform, or deck, positioned on top of structural beams which are, in turn, mounted on load cells and located in a pit. Typically, the required pit is about 5 feet deep, requiring heavy concrete sides, end walls and footings. Not only is there a high initial cost associated with such a pit, but such pits present maintenance problems, such as drainage and cleaning out of debris which accumulates in somewhat inaccessible places along the pit bottom.
Attempts have been made to devise weighbridges with a low deck height (about 10-12 inches) which can be mounted above grade or in an accessible depression slightly below the surface. Of the two types of low profile truck scales on the market at present, the more common approach is to have beams or girders on each side and undersling a shallow deck in between to receive the vehicle to be weighed. Although such arrangements require few supports (hence, few expensive load cells) they inherently require more material and fabrication operations, which results in a weighing device which is considerably more expensive than a conventional in-pit scale arrangement. Another approach is to construct an all-steel deck, or slab, using a large number of supports. Such arrangements are costly, as they involve the extensive handling and fabrication of heavy steel weldments and a large number of expensive load cells and supports.
The present invention provides a low profile truck scale which utilizes predominantly inexpensive normal concrete with a minimum of handling and fabrication to produce a rugged accurate and substantially maintenance-free truck scale. By way of background, it should be noted that research investigators looking into the design of concrete slabs for highway bridges recently have found that a concrete slab prestressed in both horizontal directions results in a durable, maintenance-free structural component. It has been further found that, if the slab is partially cored out, or waffled, from the bottom, it retains its maintenance-free performance with an efficient use of materials. However, the adaptability of such prestressed slabs to a low profile vehicle scale of the size required for long trucks presents some major problems. For example, the length of the required deck is too great to have a workable slab height. This requires the deck to be divided into several panels with intermediate supports. In such arrangements, a large number of relatively short cables would need to be prestressed. It is difficult to field tension short cables with any degree of accuracy; great care and special techniques would need to be employed. An additional problem with such arrangements is that it is difficult to design and construct the intermediate supports. Such support configurations are necessarily complex, because they must transfer the load from each panel end to the load cells without being affected by factors, such as deflections, camber and thermal expansion.